Abnormalities in language acquisition and development are common in children with autism. Significant language problems frequently persist into adulthood and are associated with poor outcome even in cognitively high-functioning individuals. Despite the striking clinical significance of the language impairment, the neural and developmental underpinnings remain largely unknown. An understanding of the biological basis of abnormal language development in autism is critical for the design of targeted interventions and treatment and improvement of adult outcome. The purpose of this study is to examine the structural development of cortical areas responsible for early stages of processing of auditory (Heschl's gyrus) and language (planum temporale) stimuli. The examination of these auditory- and language-related cortical areas is important because 1) there is currently no published detailed information about structural development of these areas during childhood in autism using longitudinal data, and 2) abnormalities in the structural development of these areas could dramatically affect subsequent language development and functioning. This study will use 3 Tesla longitudinal MRI data collected at three time points, 2.5 years apart, from children ages 3-12 at the time of their first scan, with up to three scans available per child. In Aim 1, longitudinal structural MRI data from 40 high-functioning children with autism and 20 typically developing children will be examined to compare volumetric gray and white matter development of Heschl's gyrus and gray matter development of the planum temporale. Aim 2 will examine structural-language correlates of Heschl's gyrus and planum temporale growth. Growth trajectories of individuals with autism with delayed onset of language will be compared to those with typical language onset. In addition, the ability of structural growth trajectories to predict language functioning will be tested in the autism and control groups. Language abnormalities significantly impair children, adolescents, and many adults with autism. This project will determine how longitudinal development of two key cortical areas involved in auditory and language processing differs during childhood and adolescence in those with autism compared to typical development. Abnormalities in the development of these regions will help explain why language development is abnormal, which is critical for the design of targeted interventions and treatment and improvement of language function.